Shelf



FIG. 1 is a front perspective view of a shelf showing my new design;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a rear view thereof;

FIG. 6 is a right side view thereof; and,

FIG. 7 is a top plan view thereof.

The broken lines shown in the figures represent portions of the shelf that form no part of the claimed design. 

CLAIM The ornamental design for a shelf, as shown and described. 